T Lymphocytes And Cell-mediated Immunity

Question 1

What is an antigen?

Answer 1

This is any part of an organism or substance that the body recognises as non-self.

Question 2

What type of molecules are antigens usually?

Answer 2

They are usually proteins.

Question 3

What are antigens part of?

Answer 3

They are part of the cell-surface membrane or cell walls of invading cells.

Question 4

What triggers the production of an antibody as part of the body’s defence system?

Answer 4

The presence of an antigen.

Question 5

Is phagocytosis specific or non-specific?

Answer 5

Non-specific

Question 6

What are the key features of specific immune responses?

Answer 6

They are slower at first but they can provide long-term immunity.

Question 7

What does the type of specific immune response depend upon?

Answer 7

The type of lymphocyte.

Question 8

Where are lymphocytes produced?

Answer 8

In the bone marrow.

Question 9

What produces lymphocytes?

Answer 9

Stem cells

Question 10

What are the two types of lymphocyte?

Answer 10

B lymphocytes

T lymphocytes

Question 11

Where do B lymphocytes mature?

Answer 11

In the bone marrow.

Question 12

What type of immunity are B cells associated with?

Answer 12

Humoral immunity

Question 13

Where do T cells mature?

Answer 13

In the thymus gland.

Question 14

What type of immunity are T cells associated with?

Answer 14

Cell-mediated immunity.

Question 15

What does humoral immunity involve?

Answer 15

This involves antibodies that are present in the body fluids, or “humour” such as blood plasma.

Question 16

What does cell-mediated immunity involve?

Answer 16

This involves body cells.

Question 17

Why can T cells distinguish invader cells from normal cells?

Answer 17

Phagocytes that have engulfed and hydrolysed a pathogen present some of the pathogen’s antigens on their own cell-surface membrane.
Body cells that are invaded by a virus present some of the viral antigens on their own cell-surface membrane.

Question 18

How do T cells distinguish body cells from transplanted cells?

Answer 18

Transplanted cells from individuals of the same species have different antigens on their cell-surface membrane.

Question 19

How do T cells distinguish cancer cells from normal body cells?

Answer 19

Cancer cells are different from normal body cells and present antigens on their cell-surface membrane.

Question 20

What are antigen-presenting cells?

Answer 20

These are cells that have the ability to display foreign antigens on their surface.

Question 21

What is the cellular response?

Answer 21

This is where T lymphocytes only respond to antigens that are presented on a body cell rather than to antigens within the body fluid.

Question 22

What do the receptors on each T cell respond to?

Answer 22

A single antigen.

Question 23

Are there lots of T cells or only a few?

Answer 23

There is a vast number of different types of T cell and each type responds to a different antigen.

Question 24

Summarise the response of T lymphocytes.

Answer 24

Pathogens invade body cells or are taken in by phagocytes.
The phagocyte places antigens from the pathogen on its cell-surface membrane.
Receptors on a specific T helper cell fit exactly onto these antigens.
This attachment activates the cell to divide rapidly by mitosis and form a clone of genetically identical cells.

Question 25

What do the cloned T cells do?

Answer 25

They develop into memory cells.
They stimulate the phagocytes to engulf the pathogens by phagocytosis.
Stimulate B cells to divide and secrete their antibody.
Activate cytotoxic T cells.

Question 26

What do cytotoxic Y cells kill?

Answer 26

They kill abnormal cells and body cells that have been infected by pathogens.

Question 27

How do cytotoxic T cells kill?

Answer 27

They produce a protein called perforin which makes holes in the cell surface membrane.

Question 28

What problems do the holes in the cell-surfaces membrane create?

Answer 28

The cell membrane becomes freely permeable to all substances and the cell does as a result.

Question 29

What is the action of T cells the most effective against?

Answer 29

They are most effective against viruses but the body cell has to be sacrificed (because viruses replicate inside cells) to stop the virus from multiplying and infecting more cells.